RUL versus PCE proximity: for which brick type are the values of refractoriness under load (RUL) and pyrometric cone equivalent (PCE) typically the closest in magnitude?

Introduction / Context:
Two standard high-temperature indices used for refractory selection are pyrometric cone equivalent (PCE), indicating softening without load, and refractoriness under load (RUL), indicating deformation under specified load. The closeness of these two metrics helps assess how much load degrades the effective working temperature.

Given Data / Assumptions:

• Silica bricks: high PCE but RUL notably lower due to viscous flow on load.
• Fireclay bricks: moderate PCE and often a pronounced gap to RUL.
• High alumina bricks: stronger load-bearing at temperature; RUL approaches PCE more closely.

Concept / Approach:
High alumina bricks contain phases (e.g., mullite, corundum) that sustain rigidity and resist creep at temperature. As a result, their RUL is typically nearer to their PCE than for silica or general fireclay refractories. This reduces the “penalty” when load is applied, allowing higher safe service temperatures under stress.

Step-by-Step Solution:
Compare microstructures and high-temperature creep resistance across brick classes.Identify the class with minimal RUL–PCE gap → high alumina.Select “High alumina bricks.”

Verification / Alternative check:
Material datasheets often show high alumina products with RUL values close to PCE, while silica shows larger divergence due to load sensitivity.

Why Other Options Are Wrong:
Silica / Fireclay: larger RUL reduction relative to PCE.Tar dolomite: performance depends on bonding and sintering; not generally closest.Carbon bricks: different test context; PCE terminology is for oxide refractories.

Common Pitfalls:
Assuming highest PCE implies closest RUL; the relationship depends on creep resistance.

Final Answer:
High alumina bricks